Ink, ink jet recording method, ink cartridge, and ink jet recording apparatus

ABSTRACT

An ink contains at least a pigment, wherein the pigment is C.I. Pigment Red 282, and a primary particle diameter D (nm) of the pigment and a 50%-cumulative diameter D50 (nm) in particle diameter distribution of the pigment satisfy a relation of D×0.95≦D50≦150, and a 90%-cumulative diameter D90 (nm) in particle diameter distribution of the pigment and the 50%-cumulative diameter D50 (nm) satisfy a relation of 1.5≦D90/D50≦2.5.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an ink containing C.I. Pigment Red 282,a quinacridone pigment; and an ink jet recording method, an inkcartridge, and an ink jet recording apparatus employing the ink.

2. Description of the Related Art

For recording of full-color images, generally are used a combination offour inks of subtractive three primary colors (yellow, magenta, andcyan) and a black color. To improve fastness properties of the imagerecorded by an ink jet recording method, inks (pigment inks) containinga pigment are widely used as the coloring material.

Lately, the quality of the images obtained by ink jet recording methodhas been highly improved, and is demanded to be nearly at the same levelas the image obtained by silver-halide photography. For example, theimage recorded with a pigment ink on a highly glossy recording medium (aglossy paper) tends to lower the glossiness. The glossiness of therecorded image is demanded not to be lowered with the color reproductionrange kept broader.

In particular, the human visual sensation is very sensitive to the imagein a red color region recorded with a magenta ink. Many techniques aredisclosed for improving the color development of the image recorded witha magenta ink. Pigments used for the ink jet magenta ink are disclosed,for example, in Japanese Patent Application Laid-Open No. H10-120956 andJapanese Patent Application Laid-Open No. H10-219166. For example, thereare disclosed a solid solution of quinacridone pigments different inphysical properties such as the color hue, weather fastness, and heatresistance other than the pigments having a simple chemical structuretypified by C.I. Pigment Red 122.

Further for improving the color development of the recorded image,without limitation to the magenta inks, the particle size of the pigmentand ratio of the primary particle size to the secondary particle sizeare defined (Japanese Patent Application Laid-Open No. 2004-175880 andJapanese Patent Application Laid-Open No. 2006-002141).

As described above, no conventional magenta ink is capable ofreproducing a color in the red region in the same quality as insilver-halide photography with high ink-storage stability withoutdecrease of the glossiness.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments.

SUMMARY OF THE INVENTION

The present invention intends to provide an ink which has high storagestability and is capable of recording a glossy image on a glossy paperwith high color reproducibility in the red color region in a broadercolor reproduction range. The present invention intends to provide alsoan ink jet recording method, an ink cartridge, and an ink jet recordingapparatus for recording stably a glossy image with color reproducibilityin a red color region at the same high level as in the silver-halidephotography.

The present invention is directed to an ink containing a pigment,wherein the pigment is C.I. Pigment Red 282, and a primary particlediameter D (nm) of the pigment and a 50%-cumulative diameter D₅₀ (nm) inparticle diameter distribution of the pigment satisfy a relation ofD×0.95≦D₅₀≦150, and a 90%-cumulative diameter D₉₀ (nm) in particlediameter distribution of the pigment and the 50%-cumulative diameter D₅₀(nm) satisfy a relation of 1.5≦D₉₀/D₅₀≦2.5.

According to the present invention, there is provided an ink which hashigh storage stability and is capable of recording a glossy image on aglossy paper with high color reproducibility in a red color region in abroader color reproduction range. Further, according to the presentinvention, there are provided an ink jet recording method, an inkcartridge, and an ink jet recording apparatus for recording stably aglossy image with color reproducibility in a red color region at thesame high level as in the silver-halide photography.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments.

DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail.

The inventors of the present invention studied use of quinacridonepigments, widely used as a coloring material in ink jet recording, forincreasing the chroma and glossiness of the image recorded with amagenta ink. Thereby, it was found that use of C.I. Pigment Red 282 asthe pigment enables improvement of the chroma and glossiness of theformed image. However, C.I. Pigment Red 282 can not readily be keptstable in a dispersion state in comparison with usual magenta pigments.

Therefore, the inventors of the present invention studied the optimumdispersion conditions for keeping stable the ink containing the abovepigment for a long term, that is, for improving the storage stability ofthe ink. Thereby the inventors of the present invention have found thatthe ink storage stability can be remarkably improved and the chroma andglossiness of the recorded image can be improved under the twoconditions below, and have completed the present invention.

One of the conditions for achieving the above effects with an inkcontaining C.I. Pigment 282 (hereinafter simply referred to as apigment, occasionally) is that the average diameter of the pigmentparticles (secondary particles) in a state existing in the ink is madesmaller, and the primary particles of the pigment is kept undamaged asmuch as possible. Specifically, in the ink containing C.I. Pigment 282,the primary particle diameter D (nm) of the pigment and the50%-cumulative diameter D₅₀ (nm) of the particle diameter distributionshould satisfy the relation of D×0.95≦D₅₀≦150.

The other one of the conditions for achieving the above effects is thatthe particle diameter distribution of the C.I. Pigment 282 in the ink ismade narrower or made uniform as much as possible. Specifically, theratio of the 90%-cumulative diameter D₉₀ (nm) to 50%-cumulative diameterD₅₀ (nm) in particle diameter distribution of the pigment should satisfythe relation of 1.5≦D₉₀/D₅₀≦2.5.

In the present invention, the term “average particle diameter” refers tothe average of the diameters of the pigment particles (secondaryparticles) in the state existing in the ink. The term “primary particlediameter” in the present invention refers to a particle diameter of theminimum unit of the pigment particles. Therefore, the particle diameterdistribution of the pigment in the present invention refers to theparticle diameter distribution of the pigment in a state existing in theink. Incidentally, the 50%-cumulative diameter D₅₀ (nm) in particlediameter distribution of the pigment and the 90%-cumulative diameter D₉₀(nm) thereof are occasionally referred to simply as D₅₀, and D₉₀respectively. In a state in the ink, the pigment particle of the smallparticle diameter can be formed from one primary particle. In this casethe primary particle diameter and the secondary particle diameter arethe same.

Under the above two conditions, the pigment is dispersed stably in theink to improve the storage stability of the ink, and the chroma andglossiness of the recorded image are improved. The inventors of thepresent invention consider the reason as below.

Firstly the reason is described below why the above relation between theaverage particle diameter of the pigment and the primary particlediameter of the pigment affects greatly the storage stability of thepigment and the chroma and glossiness of the recorded image. Generally,decrease of the average particle diameter of the pigment is known to beeffective for improving the chroma and glossiness of the recorded image.Actually the inventors of the present invention confirmed that thedecrease of the average particle diameter D₅₀ decreases the lightscattering by the image recorded on a recording medium and improves thechroma and glossiness of the recorded image.

However, the inventors of the present invention found that the smalleraverage particle diameter of the pigment can not necessarily improve thestorage stability of the ink significantly. The inventors investigatedthe reason for this. The impact force or shearing force applied to thepigment for pulverization will distort the crystal structure of thepigment to make the pigment particles instable to facilitate particleaggregation and to impair the long-term storage stability of the ink. Onthe other hand, when the average particle diameter of the pigment isextremely large in comparison with the primary particle diameter of thepigment, light scattering in the recorded image is influential to impairthe chroma and glossiness of the recorded image.

From the above reason, for satisfying the storage stability of the inkcontaining C.I. Pigment Red 282 and for improving the chroma andglossiness of the recorded image, the primary particle diameter D (nm)of the pigment and the 50%-cumulative diameter D₅₀ (nm) of the particlediameter distribution should satisfy the relation of D×0.95≦D₅₀≦150. AtD₅₀ more than 150, the desired chroma and glossiness of the recordedimage are not obtained, whereas at D₅₀ less than D×0.95, the storagestability of the ink are not achievable.

Next, the relation of the particle diameter distribution of the pigment(C.I. Pigment 282) with the chroma and glossiness of the recorded imagewill be described. Based on the above study, the inventors of thepresent invention investigated on the method for dispersing the pigmentto satisfy the relation between the primary particle diameter D (nm) andthe aforementioned 50%-cumulative particle diameter of the pigment:D×0.95≦D₅₀≦150. In the course of the investigation, it was found that,the chroma and glossiness of the pigment can vary even when the relationbetween the primary particle diameter and D₅₀ of the pigment is notvaried. Specifically, even with the same relation between the primaryparticle diameter and the D₅₀ of the pigment, the pigment having anarrower particle diameter distribution improves the chroma andglossiness of the recorded image. As the result of the investigationthereon, the chroma and glossiness of the recorded image depend greatlyon the surface state of the pigment layer formed on the recordingmedium. For higher chroma and higher glossiness of the image, thepigment layer should be made flatter and smoother. The inventors of thepresent invention found that a pigment having a narrower particle sizedistribution can deposit in a higher density to form a flat pigmentlayer. Thereby the pigments having the same average particle diametercan become different in the smoothness of the pigment layer depending onthe particle diameter distribution to cause difference in the chroma andglossiness of the recorded image.

Further, in addition to the above requirement, for satisfying thestorage stability of the ink containing C.I. Pigment Red 282 as thepigment and for improving the chroma and glossiness of the recordedimage, the ratio of the 90%-cumulative diameter D₉₀ (nm) to50%-cumulative diameter D₅₀ (nm) in particle diameter distribution ofthe pigment should satisfy at least the relation of D₉₀/D₅₀≦2.5.According to the findings of the inventors of the present invention, thelower the ratio of D₉₀/D₅₀, the more are the chroma and glossiness ofthe recorded image improved. However, the D₉₀/D₅₀ ratio less than 1.5 isnot preferred in view of the cost and number of the preparation steps ofthe pigment dispersion liquid. On the other hand, the pigment having theratio of D₉₀/D₅₀ more than 2.5 is not preferred since such a pigmentdoes not give the desired chroma and glossiness of the recorded image.In consideration of the above matters, the ink of the present inventionshould satisfy the relation of 1.5≦D₉₀/D₅₀≦2.5, more preferably of1.5≦D₉₀/D₅₀≦2.0.

In short, for satisfactory ink storage stability of the ink, for thehigher glossiness of an image recorded on a glossy paper, and for abroader color reproduction range in the red region, the pigment in theink should have an optimum relation between the primary particlediameter and the dispersed particle diameter and should have a narrowparticle-diameter distribution represented by the ratio of D₉₀/D₅₀.Specifically, in the ink containing C.I. Pigment 282, the primaryparticle diameter D (nm) of the pigment and the 50%-cumulative diameterD₅₀ (nm) of the particle diameter distribution should satisfy therelation of D×0.95≦D₅₀≦150, and the ratio of the 90%-cumulative diameterD₉₀ (nm) to the 50%-cumulative diameter D₅₀ (nm) in particle diameterdistribution of the pigment should satisfy the relation of1.5≦D₉₀/D₅₀≦2.5.

The primary particle diameter D (nm) in the present invention isdetermined as described below. A pigment-dispersion liquid or an ink isdiluted suitably with pure water, and the diameters of 100 or more ofthe minimum unit particles constituting the pigment particles aremeasured for the primary particle diameter by transmission electronmicroscopy or scanning electron microscopy, with image processing ifnecessary, and the measure diameters are averaged. More specifically, aprimary particle diameter of one primary particle is determined bymeasuring a short axis diameter B (nm) and a long axis diameter L (nm),and (B+L)/2 is taken as the diameter of the primary particle. Theindividual primary particle diameters of 100 or more particles aremeasured and are averaged to obtain the average primary particlediameter. Incidentally, when one pigment particle is constituted of oneprimary particle, the diameter of this pigment particle is considered tobe equal to the diameter of the primary particle. In the Examplesdescribed later, the primary particle diameter is measured by Hitachiultra-high-performance scanning electron microscope SU-70 (Hitachi HighTechnologies Co.) as the scanning electron microscope. In the presentinvention, the 50%-cumulative diameter (nm) and 90%-cumulative diameter(nm) in the pigment particle diameter distribution correspondrespectively to the average particle diameter based on the volume,namely the volume-average particle diameter. The diameters of D₅₀ andD₉₀ can be measured, for example, by a dynamic light-scattering type ofparticle distribution tester, but is not limited thereto. In Examplesdescribed later, D₅₀ and D₉₀ were measured by Nano-Track UPA150EX(manufactured by Nikkiso Co.) as the dynamic light-scattering type ofparticle distribution tester.

The difference of the present invention having essentially the aboveconstitution from prior techniques is described below. As mentioned inDescription of the Related Art, many disclosures have been made onpigment inks using a quinacridone pigment or a solid-solution thereof(Japanese Patent Application Laid-Open No. H10-120956 and JapanesePatent Application Laid-Open No. H10-219166). However, none of thedisclosures describes a pigment dispersion liquid using C.I. Pigment 282as in the present invention. Or none of them describes the relationbetween the average particle diameter in the pigment dispersion liquidand the primary particle diameter of the pigment, or the relationbetween the 90%-cumulative particle diameter and the 50%-cumulativeparticle diameter of the dispersed particles.

On the other hand, as described in above-cited Japanese PatentApplication Laid-Open No. 2004-175880 and Japanese Patent ApplicationLaid-Open No. 2006-002141, the control of the particle diameterdistribution has been investigated, regardless of the kinds of thepigments, such as the average particle diameter, the particle diameterdistribution, and the ratio of the average primary particle diameter tothe average secondary particle diameter.

Japanese Patent Application Laid-Open No. 2004-175880 defines theconstituting ratio of particles in a limited particle diameter range,but does not describe the relation between the primary particle diameterand the dispersed particle diameter. The primary particle diameterherein refers to a diameter of the minimum unit of the particledistinguished clearly from other particles. The smaller diameter of theparticle than the primary particle diameter is caused by destruction ofthe pigment crystal. This impairs the dispersion stability of thepigment. For the dispersion stability, the dispersed particle diametershould be balanced with the primary particle diameter of the pigment.Japanese Patent Application Laid-Open No. 2006-002141 cited abovedescribes the ratio of the average primary particle diameter to theaverage secondary particle diameter. The secondary particles are formedby aggregation of the primary particles existing in the dispersionliquid. The particle size testers measure the diameters of the secondaryparticles. However, according to the investigation by the inventors ofthe present invention, with the average primary particle diametercontrolled to be 50 nm or less, the interaction among the primaryparticles becomes stronger to make difficult the dispersion to decreasethe dispersion stability of the pigment dispersion.

<Ink>

The constituents of the ink of the present invention are described belowin detail.

(Pigment)

The pigment employed in the present invention is C.I. Pigment Red 282.The primary particle diameter D (nm) ranges preferably from 50 nm ormore to 130 nm or less. The primary particle diameter D of less than 50nm is not preferred since the particle of a smaller diameter can impairthe lightfastness of the pigment to lower the lightfastness of therecorded image, or requires a larger amount of the polymer for keepingthe dispersion stability. The polymer in a large amount in the ink willimpair the smoothness of the recorded image and give insufficient chromaand glossiness of the recorded image. On the other hand, the primaryparticle diameter D more than 130 nm is not preferred since theexcessively larger average particle diameter of the pigment can impairthe chroma and glossiness of the recorded image.

The content (mass %) of the pigment in the ink is preferably in therange from 0.1 mass % or more to 10.0 mass % or less, more preferablyfrom 0.5 mass % or more to 5.0 mass % or less with respect to the totalmass of the ink. Within the above range of the content of the pigment,both the image density of the recorded image and the ink ejectionstability in the ink jet recording can be kept at higher levels.

(Polymer)

The ink of the present invention contains preferably a polymer, and canbe prepared with a pigment dispersion liquid containing the specifiedpigment and a polymer. In the present invention, to solve the technicalproblems, in particular, in consideration of scratch resistance of theimage recorded on a glossy paper, the pigment is dispersed preferably ina satisfactory state by a polymer. In the present invention, “a pigmentdispersed by a polymer” includes not only polymer-dispersion typepigments which have a polymer adsorbed on the surface of the pigmentparticles but also the pigments mentioned below. Specifically, thepigments include polymer-bonding type self-dispersible pigments havingan organic radical (polymer) having a polymer structure bondedchemically to the pigment surface, and microcapsule type pigments coatedby an organic high polymer. As the results of the investigation by theinventors of the present invention, the polymer-dispersed pigments arethe most suitable, and polymer-bonding type self-dispersible pigmentsare also preferred. This is because the polymer bonded chemically to thesurface of the pigment particle stabilizes the dispersion.

The polymer for dispersing the pigment is formed by polymerization of amaterial containing a monomer like the ones mentioned below. The monomerfor the polymer includes styrene, and α-methylstyrene; hydrophobicmonomers having a carboxy group such as n-butyl acrylate, n-hexylacrylate, and benzyl methacrylate; hydrophilic monomers having acarboxyl group such as acrylic acid, methacrylic acid, crotonic acid,ethacrylic acid, propylacrylic acid, isopropylacrylic acid, itaconicacid, and fumaric acid; hydrophilic monomers having a sulfonic acidgroup such as styrene-sulfonic acid, sulfonic acid-2-propylacrylamide,ethyl acrylic acid-2-suofonate, ethyl methacrylic acid-2-sulfonate,butylacrylamide-sulfonic acid; and hydrophilic monomers having aphosphonic acid group such as ethyl methacrylic acid-2-phosphonate, andethyl acrylic acid-2-phosphonate.

The specified pigment in the present invention cannot readily be keptstably in a dispersion state in comparison with usual pigments.Therefore, in the present invention, for dispersing the pigment, apolymer formed by polymerization of a material containing at least anacrylic type monomer, an acrylic polymer, is used which is resistant tohydrolysis and capable of improving the dispersion stability. Further, apolymer is preferred which is formed by polymerization of a materialcontaining a nonionic group such as an ethylene oxide group or apropylene oxide group or a mixture thereof, namely a polymer having anonionic unit in the structure. In recording with the ink containing thepigment dispersed with the aid of the polymer, the aggregation of thepigment can be retarded effectively in comparison with the ink pigmentdispersed by the polymer having no nonionic unit, and the glossiness ofthe recorded image can be improved remarkably.

In the present invention, for improving further the glossiness of therecorded image, the polymer has an acid value in the range preferablyfrom 50 mgKOH/g or more to 300 mgKOH/g or less. Within the above rangeof the acid value, the surface of the recorded image is formed flatterand smoother to improve the glossiness of the image. The polymer havingthe acid value of less than 50 mgKOH/g can lower the dispersionstability of the pigment owing to electrostatic repulsion to increasethe ink viscosity on recording of the image, resulting in a roughsurface of the recorded image to lower the lower chroma and glossinessof the image. On the other hand, the polymer having the acid value ofmore than 300 mgKOH/g can be less adsorbable to the pigment particlesurface to cause penetration of the desorbed polymer into the recordingmedium to result in decrease of the polymer on the surface of therecorded image to decrease the glossiness. The polymer has aweight-average molecular weight preferably in the range from 1,000 ormore to 30,000 or less, more preferably from 3,000 or more to 15,000 orless.

The content of the pigment in the ink is preferably in the range of 0.30times or more to 10.0 times or less the polymer content by the mass.That is, (pigment content)/(polymer content)=0.30 or more to 10.0 orless (by mass ratio). Herein, the contents of the polymer and thepigment are based on the total mass of the ink. Within the above massratio ranging from 0.30 times or more to 10.0 times or less, thedispersion state of the pigment can be kept stable. At the above massratio less than 0.30 times, the amount of the polymer is excessivelylarge relative to the amount of the pigment, which tends to causeinsufficiency in the chroma and glossiness of the recorded image. On theother hand, at the above mass ratio more than 10.0 times, the amount ofthe polymer is insufficient relative to the amount of the pigment, whichtends to make the dispersion nonuniform in the production of the pigmentdispersion to make difficult the production of the pigment dispersionand make insufficient the ink storage stability. In the presentinvention, the mass ratio is particularly preferably 2.0 times or moreto improve remarkably the glossiness of the recorded image.

(Aqueous Medium)

The ink of the present invention contains preferably an aqueous mediumconstituted of a mixed solvent of water and a water-soluble organicsolvent. The water is preferably a deionized water like ion-exchangedwater or pure water. The content (mass %) of the water in the ink ispreferably in the range from 50.0 mass % or more to 95 mass % or lesswith respect to the total mass of the ink.

The content (mass %) of the water-soluble organic solvent in the inkranges preferably from 3.0 mass % or more to 50.0 mass % or less withrespect to the total mass of the ink. One or more water-soluble organicsolvents are used. The water-soluble organic solvent includes glycolethers such as diethylene glycol monomethyl (or ethyl)ether, andtriethylene glycol monoethyl (or butyl)ether; alkanols of 1-4 carbonssuch as methanol, ethanol, propanol, isopropanol, n-butanol,sec-butanol, isobutanol, and t-butanol; carboxamides such asN,N-dimethylformamide, and N,N-dimethylacetamide; ketones andketoalcohols such as acetone, methyl ethyl ketone, and2-methyl-2-hydroxypentan-4-one; cyclic ethers such as tetrahydrofuran,and dioxane; glycols such as ethylene glycol, diethylene glycol,triethylene glycol, tetraethylene glycol, propylene glycol, and butyleneglycol; polyethylene glycols having an average molecular weight rangingfrom 200 to 2,000, specifically a molecular weight of 200, 400, 600,1000, and 2000; acetylene glycol derivatives; polyhydric alcohols suchas glycerin, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, and1,2,6-hexane triol; heterocyclic compounds such as 2-pyrrolidone,N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, andN-methylmorpholine; and sulfur-containing compounds such asthiodiglycol, and dimethylsulfoxide.

(Other Components)

The ink may contain, in addition to the above components, amoisture-retaining compound such as urea, a urea derivative,trimethylolpropane and trimethylolethane, which are solid at normaltemperature. The content (mass %) of such a compound ranges preferablyfrom 0.1 mass % or more to 20.0 mass % or less, more preferably from 3.0mass % or more to 10.0 mass % or less with respect to the total mass ofthe ink.

Further the ink may contain, in addition to the above components, amiscellaneous additive such as a surfactant, a pH-controller, arust-preventing agent, an antiseptic agent, an anti-fungus agent, anantioxidant, and a reduction-preventing agent.

<Ink Jet Recording Method, Ink Cartridge, and Ink Jet RecordingApparatus>

The ink jet recording method records an image on a recording medium byejection of the ink described above through a recording head of an inkjet system. The ink jet recording apparatus of the present invention isequipped with an ink storage portion for storing the ink, and arecording head for ejection of the ink. The ink mentioned above of thepresent invention is stored in the ink storage portion. The ink of thepresent invention is effective in a recording head or an ink jetrecording apparatus of bubble-Jet® type of the ink jet system. Aconventional ink jet recording method and a conventional ink jetrecording apparatus may be employed, provided that the ink of thepresent invention is used. In the present invention, the “recording”includes embodiments of recording with the ink of the present inventionon a recording medium like a glossy paper or a plain paper, and printingwith the ink of the present invention on a non-liquid-absorbent mediumlike a glass plate, a plastic sheet, or a film.

The ink cartridge of the present invention has an ink storage portionfor storing the above-mentioned ink of the present invention. In aconstruction of the ink cartridge, the ink storage portion isconstituted of an ink storing chamber for storing a liquid ink, and maybe equipped with a room for storing a negative pressure-generatingmember for retaining the ink therein by applying a negative pressure ifnecessary. Otherwise, the ink cartridge may have an ink storage portionconstituted of an ink storage portion capable of storing the entire inkby the negative-pressure-generating member without the ink storing room.Further, the ink cartridge may be constituted of an ink storage portionand a recording head.

<Production of Pigment Dispersion Liquid>

The process for producing the pigment dispersion liquid is described forproducing the ink of the present invention. The ink containing thespecified pigment having the characteristic particle diameter defined inthe present invention can be produced readily by use of the pigmentdispersion liquid produced by the production process described below.

The pigment dispersion liquid can be produced by a dispersion apparatus,by suitably controlling the dispersion conditions such as the dispersiontime, the peripheral speed, the kind of the medium, and the particlediameter. The dispersion apparatus includes roll mills, bead mills,paint shakers, sand mills, agitator mills, Nanomizer®, homogenizers,micro-fluidizers, ultimizers, and ultrasonic dispersing machines.

As the results of the investigation, the inventors of the presentinvention have found that, for obtaining the ratio of D₉₀/D₅₀ in therange defined in the present invention, application of a sufficientshearing force to the dispersed pigment is effective in the step of apreliminary dispersion of the pigment. Specifically, the pigmentdispersion liquid is prepared preferably through the first to thirdsteps described below.

(First Step)

An emulsion composition containing a polymer, a neutralizing agent, anorganic solvent, and water, and the pigment are mixed to obtain amixture containing non-volatile component at a content ranging from 30mass % to 50 mass %, and having a viscosity ranging from 50 mPa·s to1,000 mPa·s at 25° C.

(Second Step)

A preliminary dispersion liquid is prepared which has a viscosityranging from 50 mPa·s to 500 mPa·s at 25° C. In this step the mixtureobtained in the first step is treated by a media less dispersing machinelike a high-pressure homogenizer with a net integrated power in therange from 0.50 kWh/kg to 10.00 kWh/kg of the mixture.

(Third Step)

The preliminary dispersion liquid prepared in the above second Step istreated for dispersion.

EXAMPLES

The present invention is descried below in more detail with reference toExamples and Comparative Examples without limiting the invention withinthe gist of the present invention. In the descriptions below, the terms“part” and “%” are based on mass, unless otherwise mentioned.

The viscosity is measured by a B-type viscometer (Toki Sangyo Co.) at25° C. The primary particle diameter D (nm) is an average of thediameters of 100 or more primary particles measured by the method below.The pigment dispersion liquid is diluted with pure water. The diluteddispersion liquid is observed with a Hitachi ultra-high-performancescanning electron microscope SU-70 (Hitachi High Technologies Co.), andthe pigment particles of the minimum unit size are image-processed andobserved for 100 or more particles. The 50%-cumulative diameter D₅₀ (nm)and the 90%-cumulative diameter D₉₀ (nm) in the pigment particlediameter distribution is measured by Nano-Track UPA150EX (Nikkiso Co.)under the measurement conditions: solvent, water; solvent refractiveindex, 1.333; solvent viscosity, 1.002 (20° C.) and 0.7971 (30° C.);particle transmissivity, transmissive; particle refractive index, 1.51;particle shape, nonspherical. The C.I. Pigment Red 282 is Ciba IRGAZINMAGENTA 2012 (Ciba Co.).

<Production of Pigment Dispersion Liquid>

(Pigment Dispersion Liquid 1)

A portion of 10 parts (solid matter) of C.I. Pigment Red 282 was groundand treated with an organic solvent in a conventional manner to obtainPigment A having a primary particle diameter D of 110 nm. As the polymer(dispersant), Polymer A was prepared by synthesis from 50 parts ofstyrene, 39 parts of n-butyl acrylate, and 30 parts of methacrylic acidin a conventional manner. The resulting polymer had an acid value of 195mgKOH/g, and was a random polymer having a weight-average molecularweight of 9,000. The polymer was neutralized with an equivalent amountof an aqueous potassium hydroxide solution to obtain Polymer A. PigmentDispersion Liquid 1 was obtained by use of the above Pigment A andPolymer A through the first to third steps below. Incidentally, First toThird Steps mentioned later in the production of other pigmentdispersion liquids refer to the above first to third steps. Theproduction conditions and the properties of the resulting pigmentdispersion liquid shown in Table 1.

(First Step)

180 parts of Pigment A, 90 parts of Polymer A, and 330 parts ofdeionized water were mixed by a Homomixer (manufactured by Primix Co.)to obtain a slurry (mixture) having a viscosity of 200 mPa·s.

(Second Step)

The slurry obtained in the above First Step was stirred by a circulationtype of homogenizer (Clearmix (M. Tech Co.): referred to as CLM inTables) for one hour to obtain a preliminary dispersion liquid. The netintegral power applied to the slurry was 0.75 kWh/kg. The viscosity ofthe resulting preliminary dispersion liquid was 1.00 mPa·s

(Third Step)

The preliminary dispersion liquid obtained in the above Second Step wasdispersed by a circulation type of bead mill (referred to simply as BMin Tables) under the conditions of the packing ratio of 85% of zirconiabeads of 0.1 mm-diameter, and a peripheral velocity of 8 m/s for 115minutes to obtain Pigment Dispersion Liquid 1. The bead mill employedwas MiniCer (Ashizawa Fine Tech Co.). The resulting Pigment DispersionLiquid 1 contained the pigment of D of 110 nm, D₅₀ of 112 nm, D₉₀ of 194nm, and D₉₀/D₅₀ of 1.7 at a content of 30.0%, and the polymer at acontent of 15.0%.

(Pigment Dispersion Liquid 2)

Pigment Dispersion Liquid 2 was prepared in the same manner as PigmentDispersion Liquid 1 except that, in Third Step, the diameter of thezirconia beads was changed to 0.2 mm, and the dispersion time waschanged to 100 minutes. The resulting Pigment Dispersion Liquid 2contained the pigment of D of 110 nm, D₅₀ of 148 nm, D₉₀ of 220 nm, andD₉₀/D₅₀ of 1.5 at a content of 30.0%, and the polymer at a content of15.0%.

(Pigment Dispersion Liquid 3)

Pigment Dispersion Liquid 3 was prepared in the same manner as PigmentDispersion Liquid 1 except that, in Third Step, the diameter of thezirconia beads was changed to 0.05 mm, and the dispersion time waschanged to 110 minutes. The resulting Pigment Dispersion Liquid 3contained the pigment of D of 110 nm, D₅₀ of 110 nm, D₉₀ of 273 nm, andD₉₀/D₅₀ of 2.5 at a content of 30.0%, and the polymer at a content of15.0%.

(Pigment Dispersion Liquid 4)

Pigment Dispersion Liquid 4 was prepared in the same manner as PigmentDispersion Liquid 1 except that, in Second Step, the net integratedpower applied to the slurry was changed to 1.50 kWh/kg, and in ThirdStep, the diameter of the zirconia beads was changed to 0.05 mm, and thedispersion time was changed to 130 minutes. The resulting PigmentDispersion Liquid 4 contained the pigment of D of 110 nm, D₅₀ of 109 nm,D₉₀ of 162 nm, and D₉₀/D₅₀ of 1.5 at a content of 30.0%, and the polymerat a content of 15.0%.

(Pigment Dispersion Liquid 5)

Pigment Dispersion Liquid 5 was prepared in the same manner as PigmentDispersion Liquid 1 except that, in Second Step, the net integratedpower applied to the slurry was changed to 0.50 kWh/kg, and in ThirdStep, the diameter of the zirconia beads was changed to 0.2 mm, and thetype of the bead mill was changed to a multiple path type. The resultingPigment Dispersion Liquid 5 contained the pigment of D of 110 nm, D₅₀ of145 nm, D₉₀ of 360 nm, and D₉₀/D₅₀ of 2.5 at a content of 30.0%, and thepolymer at a content of 15.0%.

(Pigment Dispersion Liquid 6)

Pigment Dispersion Liquid 6 was prepared in the same manner as PigmentDispersion Liquid 1 except that, in Second Step, the net integratedpower applied to the slurry was changed to 1.00 kWh/kg, and in ThirdStep, the diameter of the zirconia beads was changed to 0.05 mm. Theresulting Pigment Dispersion Liquid 6 contained the pigment of D of 110nm, D₅₀ of 109 nm, D₉₀ of 216 nm, and D₉₀/D₅₀ of 2.0 at a content of30.0%, and the polymer at a content of 15.0%.

(Pigment Dispersion Liquid 7)

Pigment Dispersion Liquid 7 was prepared in the same manner as PigmentDispersion Liquid 1 except that, in Second Step, the net integratedpower applied to the slurry was changed to 0.60 kWh/kg, and in ThirdStep, the diameter of the zirconia beads was changed to 0.2 mm. Theresulting Pigment Dispersion Liquid 7 contained the pigment of D of 110nm, D₅₀ of 150 nm, D₉₀ of 295 nm, and D₉₀/D₅₀ of 2.0 at a content of30.0%, and the polymer at a content of 15.0%.

(Pigment Dispersion Liquid 8)

A portion of 10 parts (solid matter) of a press cake of C.I. Pigment Red282 was grounded and was treated with an organic solvent in aconventional manner to prepare Pigment B having a primary particlediameter D of 53 nm. Pigment Dispersion Liquid 8 was prepared in thesame manner as in Pigment Dispersion Liquid 1 except that, in FirstStep, the Pigment A used in production of Pigment Dispersion Liquid 1was replaced by the above Pigment B, and in Third Step, the dispersiontime was changed to 110 minutes. The resulting Pigment Dispersion Liquid8 contained the pigment of D of 53 nm, D₅₀ of 82 nm, D₉₀ of 165 nm, andD₉₀/D₅₀ of 2.0 at content of 30.0%, and the polymer at a content of15.0%.

(Pigment Dispersion Liquid 9)

A portion of 10 parts (solid matter) of a press cake of C.I. Pigment Red282 was grounded and was treated with an organic solvent in aconventional manner to prepare Pigment C containing a primary particlediameter D of 125 nm. Pigment Dispersion Liquid 9 was prepared in thesame manner as in Pigment Dispersion Liquid 1 except that, in FirstStep, the Pigment A was replaced by the above Pigment C, and in ThirdStep, the dispersion time was changed to 175 minutes. The resultingPigment Dispersion Liquid 9 contained the pigment of D of 125 nm, D₅₀ of137 nm, D₉₀ of 212 nm, and D₉₀/D₅₀ of 1.5 at a content of 30.0%, and thepolymer at a content of 15.0%.

(Pigment Dispersion Liquid 10)

A portion of 10 parts (solid matter) of a press cake of C.I. Pigment Red282 was grounded and was treated with an organic solvent in aconventional manner to prepare Pigment D having a primary particlediameter D of 135 nm. Pigment Dispersion Liquid 10 was prepared in thesame manner as in Pigment Dispersion Liquid 1 except that, in FirstStep, the Pigment A was replaced by the above Pigment D, and in ThirdStep, the dispersion time was changed to 190 minutes. The resultingPigment Dispersion Liquid 10 contained the pigment of D of 135 nm, D₅₀of 145 nm, D₉₀ of 246 nm, and D₉₀/D₅₀ of 1.7 at a content of 30.0%, andthe polymer at a content of 15.0%.

(Pigment Dispersion Liquid 11)

A portion of 10 parts (solid matter) of a press cake of C.I. Pigment Red282 was grounded and was treated with an organic solvent in aconventional manner to prepare Pigment E having a primary particlediameter D of 45 nm. Pigment Dispersion Liquid 11 was prepared in thesame manner as in Pigment Dispersion Liquid 1 except that, in FirstStep, the Pigment A was replaced by the above Pigment E, and in ThirdStep, the dispersion time was changed to 100 minutes. The resultingPigment Dispersion Liquid 11 contained the pigment of D of 45 nm, D₅₀ of73 nm, D₉₀ of 146 nm, and D₉₀/D₅₀ of 2.0 at a content of 30.0%, and thepolymer at a content of 15.0%.

(Pigment Dispersion Liquid 12)

Pigment Dispersion Liquid 12 was prepared in the same manner as PigmentDispersion Liquid 1 except that Polymer A in First Step was replaced byPolymer B mentioned below, and the dispersion time in Third Step waschanged to 110 minutes. This Polymer B was prepared by polymerizing 40parts of styrene, 52.3 parts of n-butyl acrylate and 7.7 parts ofmethacrylic acid in a conventional manner to obtain a random copolymerhaving an acid value of 50 mgKOH/g and a weight-average molecular weightof 8,800, and neutralizing this polymer with an equivalent amount of anaqueous potassium hydroxide solution. The resulting Pigment DispersionLiquid 12 contained the pigment of D of 110 nm, D₅₀ of 120 nm, D₉₀ of226 nm, and D₉₀/D₅₀ of 1.9 at a content of 30.0%, and the polymer at acontent of 15.0%.

(Pigment Dispersion Liquid 13)

Pigment Dispersion Liquid 13 was prepared in the same manner as PigmentDispersion Liquid 1 except that Polymer A in First Step was replaced byPolymer C mentioned below, and the dispersion time in Third Step waschanged to 100 minutes. This Polymer C was prepared by polymerizing 40parts of styrene, 17 parts of n-butyl acrylate and 43 parts ofmethacrylic acid in a conventional manner to obtain a random copolymerhaving an acid value of 280 mgKOH/g and a weight-average molecularweight of 9,100, and neutralizing this copolymer with an equivalentamount of an aqueous potassium hydroxide solution. The resulting PigmentDispersion Liquid 13 contained the pigment of D of 110 nm, D₅₀ of 108nm, D₉₀ of 194 nm, and D₉₀/D₅₀ of 1.8 at a content of 30.0%, and thepolymer at a content of 15.0%.

(Pigment Dispersion Liquid 14)

Pigment Dispersion Liquid 14 was prepared in the same manner as PigmentDispersion Liquid 1 except that Polymer A in First Step was replaced byPolymer D mentioned below, and the dispersion time in Third Step waschanged to 100 minutes. This Polymer D was prepared by polymerizing 40parts of styrene, 15 parts of n-butyl acrylate, 25 parts of methacrylicacid, and 20 parts of polyethylene glycol monomethacrylate in aconventional manner to obtain a random copolymer having an acid value of160 mgKOH/g and a weight-average molecular weight of 8,600, andneutralizing this copolymer with an equivalent amount of an aqueouspotassium hydroxide solution. The resulting Pigment Dispersion Liquid 14contained the pigment of D of 110 nm, D₅₀ of 112 nm, D₉₀ of 212 nm, andD₉₀/D₅₀ of 1.9 at a content of 30.0%, and the polymer at a content of15.0%.

(Pigment Dispersion Liquid 15)

A slurry was prepared through First Step by use of Polymer E mentionedbelow in place of Polymer A, the slurry having viscosity of 300 mPa·s.Then through Second Step, with this slurry, preliminary dispersionliquid was obtained which had a viscosity of 300 mPa·s. Further PigmentDispersion Liquid 15 was obtained through Third Step in the same manneras in Pigment Dispersion Liquid 1 except that the dispersion time waschanged to 110 minutes. The above-mentioned Polymer E was prepared bypolymerizing 40 parts of styrene, 53.1 parts of n-butyl acrylate, and6.9 parts of methacrylic acid, in a conventional manner to obtain arandom copolymer having an acid value of 45 mgKOH/g and a weight-averagemolecular weight of 8,600, and neutralizing this copolymer with anequivalent amount of an aqueous potassium hydroxide solution. Theresulting Pigment Dispersion Liquid 15 contained the pigment of D of 110nm, D₅₀ of 145 nm, D₉₀ of 293 nm, and D₉₀/D₅₀ of 2.0 at a content of30.0%, and the polymer at a content of 15.0%.

(Pigment Dispersion Liquid 16)

A slurry was prepared through First Step by use of Polymer F mentionedbelow in place of Polymer A, the slurry having viscosity of 180 mPa·s.Then through Second Step, with this slurry, preliminary dispersionliquid was obtained which had a viscosity of 90 mPa·s. Further PigmentDispersion Liquid 16 was obtained through Third Step in the same manneras in Pigment Dispersion Liquid 1 except that the dispersion time waschanged to 100 minutes. The above-mentioned Polymer F was prepared bypolymerizing 40 parts of styrene, 11.6 parts of n-butyl acrylate, and48.4 parts of methacrylic acid, in a conventional manner to obtain arandom copolymer having an acid value of 315 mgKOH/g and aweight-average molecular weight of 9,200, and neutralizing thiscopolymer with an equivalent amount of an aqueous potassium hydroxidesolution. The resulting Pigment Dispersion Liquid 16 contained thepigment of D of 110 nm, D₅₀ of 115 nm, D₉₀ of 173 nm, D₉₀/D₅₀ of 1.5 ata content of 30.0%, and the polymer at a content of 15.0%.

(Pigment Dispersion Liquid 17)

Pigment Dispersion Liquid 17 was prepared in the same manner as PigmentDispersion Liquid 1 except that, in First Step, a slurry having aviscosity of 150 mPa·s was prepared by use of 54 parts of Polymer A, 180parts of Pigment A, and 366 parts of ion-exchanged water, and in SecondStep, a preliminary dispersion liquid having a viscosity of 80 mPa·s wasprepared by use of the slurry. The resulting Pigment Dispersion Liquid17 contained the pigment of D of 110 nm, D₅₀ of 128 nm, D₉₀ of 250 nm,and D₉₀/D₅₀ of 2.0 at a content of 30.0%, and the polymer at a contentof 9.0%.

(Pigment Dispersion Liquid 18)

Pigment Dispersion Liquid 18 was prepared in the same manner as PigmentDispersion Liquid 1 except that, in First Step, a slurry having aviscosity of 250 mPa·s was prepared by use of 270 parts of Polymer A, 90parts of Pigment A, and 240 parts of ion-exchanged water, and in SecondStep, a preliminary dispersion liquid having a viscosity of 150 mPa·swas prepared by use of this slurry. The resulting Pigment DispersionLiquid 18 contained the pigment of D of 110 nm, D₅₀ of 118 nm, D₉₀ of190 nm, and D₉₀/D₅₀ of 1.6 at a content of 15.0%, and the polymer at acontent of 45.0%.

(Pigment Dispersion Liquid 19)

Pigment Dispersion Liquid 19 was prepared in the same manner as PigmentDispersion Liquid 1 except that, in First Step, a slurry having aviscosity of 280 mPa·s was prepared by use of 315 parts of Polymer A, 90parts of Pigment A, and 195 parts of ion-exchanged water, and in SecondStep, a preliminary dispersion liquid having a viscosity of 160 mPa·swas prepared by use of this slurry. The resulting Pigment DispersionLiquid 19 contained the pigment of D of 110 nm, D₅₀ of 132 nm, D₉₀ of243 nm, and D₉₀/D₅₀ of 1.8 at a content of 15.0%, and the polymer at acontent of 52.5%.

(Pigment Dispersion Liquid 20)

The pigment modified as described below was used. Pigment A which hadbeen modified by 4-aminobenzoic acid was further modified by bondingthereto a copolymer of styrene/n-butyl-acrylate/methacrylic-acidsynthesized in a conventional method and having an aminophenyl group asan end group. More specifically, 200 parts of Pigment A modified by4-aminobenzoic acid and 1,000 parts of an aqueous 5% solution of theabove bonding polymer were kept at 55° C. in a reactor and stirred at arotation speed of 300 rpm for 20 minutes. Then 30 parts of 25% sodiumnitrite solution was added dropwise thereto in 15 minutes, and thereto100 parts of ion-exchanged water was added. The mixture was furtherallowed to react at 60° C. for 2 hours. The pH of the reaction mixturewas adjusted to 10 to 11 by addition of an aqueous 1.0N potassiumhydroxide solution with stirring. Therefrom modified Pigment A havingtwo kinds of atomic groups bonded chemically thereto was obtained bydesalting, purification, and coarse particle removal of the abovereaction mixture. Pigment dispersion Liquid 20 was obtained in the samemanner as Pigment Dispersion Liquid 1 except that the modified Pigment Awas used without using the polymer under the conditions shown inTable 1. In Table 1, the mixed amount in Pigment Dispersion Liquid 20denotes the amount of the polymer bonded to 100 parts of the pigment.The resulting Pigment Dispersion Liquid 20 contained the pigment of D of110 nm, D₅₀ of 115 nm, D₉₀ of 217 nm, and D₉₀/D₅₀ of 1.9 at a content of10.0%.

(Pigment Dispersion Liquid 21)

Pigment Dispersion Liquid 21 was prepared in the same manner as PigmentDispersion Liquid 1 except that, in First Step, a slurry having aviscosity of 110 mPa·s was prepared by use of 9 parts of Polymer A, 180parts of Pigment A, and 411 parts of ion-exchanged water, and in SecondStep, a preliminary dispersion liquid having a viscosity of 55 mPa·s wasprepared from the slurry. The resulting Pigment Dispersion Liquid 21contained the pigment of D of 110 nm, D₅₀ of 140 nm, D₉₀ of 278 nm, andD₉₀/D₅₀ of 2.0 at a content of 30.0%, and the polymer at a content of3.0%.

(Pigment Dispersion Liquid 22)

Pigment Dispersion Liquid 22 was prepared in the same manner as PigmentDispersion Liquid 1 except that, in First Step, a slurry having aviscosity of 100 mPa·s was prepared from 8.64 parts of Polymer A, 180parts of Pigment A, and 411.36 parts of ion-exchanged water, and inSecond Step, a preliminary dispersion liquid having a viscosity of mPa·swas prepared from the slurry. The resulting Pigment Dispersion Liquid 22contained the pigment of D of 110 nm, D₅₀ of 140 nm, D₉₀ of 293 nm, andD₉₀/D₅₀ of 2.1 at a content of 30.0%, and the polymer at a content of2.9%.

(Pigment Dispersion Liquid 23)

Pigment Dispersion Liquid 23 was prepared in the same manner as PigmentDispersion Liquid 1 except that, in First Step, a slurry having aviscosity of 200 mPa·s was prepared from 30 parts of Polymer A, 60 partsof Pigment A, and 510 parts of ion-exchanged water, and in Second Step,the net integrated power was changed to 0.30 kWh/kg to obtain apreliminary dispersion liquid having a viscosity of 10 mPa·s from theslurry, and further in Third Step, the dispersion was conducted by amultiple type of bead mill with zirconia beads of 0.2 mm diameter. Theresulting Pigment Dispersion Liquid 23 contained the pigment of D of 110nm, D₅₀ of 155 nm, D₉₀ of 377 nm, and D₉₀/D₅₀ of 2.4 at a content of10.0%, and the polymer at a content of 5.0%.

(Pigment Dispersion Liquid 24)

Pigment Dispersion Liquid 24 was prepared in the same manner as PigmentDispersion Liquid 23 except that the diameter of the zirconia beads usedin Third Step was changed to 0.1 mm. The resulting Pigment DispersionLiquid 24 contained the pigment of D of 110 nm, D₅₀ of 115 nm, D₉₀ of308 nm, and D₉₀/D₅₀ of 2.7 at a content of 10.0%, and the polymer at acontent of 5.0%.

(Pigment Dispersion Liquid 25)

Pigment Dispersion Liquid 25 was prepared in the same manner as PigmentDispersion Liquid 23 except that the net integrated power applied to theslurry in Second Step was changed to 1.50 kWh/kg, and the diameter ofthe zirconia beads used in Third Step was changed to 0.05 mm. Theresulting Pigment Dispersion Liquid 25 contained the pigment of D of 110nm, D₅₀ of 98 nm, D₉₀ of 194 nm, and D₉₀/D₅₀ of 2.0 at a content of10.0%, and the polymer at a content of 5.0%.

(Pigment Dispersion Liquid 26)

Pigment Dispersion Liquid 26 was prepared in the same manner as PigmentDispersion Liquid 1 except that the operation of Third Step was notconducted. The resulting Pigment Dispersion Liquid 26 contained thepigment of D of 110 nm, D₅₀ of 300 nm, D₉₀ of 1,000 nm, and D₉₀/D₅₀ of3.3 at a content of 10.0%, and the polymer at a content of 5.0%.

Table 1 shows collectively the constitutions of the pigment dispersionliquids and the processes of the production thereof. Incidentally someof the water-soluble organic solvents and components of the additives inthe ink can change the particle diameter of the dispersed pigment, butactually the change is negligible. Therefore, the dimensions of D, D₅₀,and D₉₀ of the pigment particles in ink were the same as those in thepigment dispersion liquid.

TABLE 1 Preparation Conditions Pigment Dispersion Liquid 1 2 3 4 5 6 7Pigment Kind of Pigment A A A A A A A Polymer kind of Polymer A A A A AA A Acid Value [mgKOH/g] 195 195 195 195 195 195 195 Wt-av. MolecularWeght 9,000 9,000 9,000 9,000 9,000 9,000 9,000 Mixed Amount (*1) 50 5050 50 50 50 50 Dispersion Viscosity in Step 1 [mPa · s] 200 200 200 200200 200 200 Conditions Dispersion Apparatus in Step 2 CLM CLM CLM CLMCLM CLM CLM Viscosity in Step 2 [mPa · s] 100 100 100 100 100 100 100Integrated Power in Step 2 0.75 0.75 0.75 1.50 0.50 1.00 0.60 [kWh/kg]Operation Mode in Step 2 circltn circltn circltn circltn circltn circltncircltn Dispersion Apparatus in Step 3 BM BM BM BM BM BM BM OperationMode in Step 3 circltn circltn circltn circltn pass circltn circltnMedium Diameter in Step 3 0.1 0.2 0.05 0.05 0.2 0.05 0.2 [mm] PropertiesPrimary Particle Diameter D 110 110 110 110 110 110 110 of [nm] PigmentD₅₀ [a · snm] 112 148 110 109 145 109 150 D₉₀ [a · snm] 194 220 273 162360 216 295 D₉₀/D₅₀ 1.7 1.5 2.5 1.5 2.5 2.0 2.0 Pigment DispersionLiquid 8 9 10 11 12 13 Pigment Kind of Pigment B C D E A A Polymer kindof Polymer A A A A B C Acid Value [mgKOH/g] 195 195 195 195 50 280Wt-av. Molecular Weght 9,000 9,000 9,000 9,000 8,800 9,100 Mixed Amount(*1) 50 50 50 50 50 50 Dispersion Viscosity in Step 1 [mPa · s] 200 200200 200 200 200 Conditions Dispersion Apparatus in Step 2 CLM CLM CLMCLM CLM CLM Viscosity in Step 2 [mPa · s] 100 100 100 100 100 100Integrated Power in Step 2 0.75 0.75 0.75 0.75 0.75 0.75 [kWh/kg]Operation Mode in Step 2 circltn circltn circltn circltn circltn circltnDispersion Apparatus in Step 3 BM BM BM BM BM BM Operation Mode in Step3 circltn circltn circltn circltn circltn circltn Medium Diameter inStep 3 0.1 0.1 0.1 0.1 0.1 0.1 [mm] Properties Primary Particle DiameterD 53 125 135 45 110 110 of [nm] Pigment D₅₀ [a · snm] 82 137 145 73 120108 D₉₀ [a · snm] 165 212 246 146 226 194 D₉₀/D₅₀ 2.0 1.5 1.7 2.0 1.91.8 (*1) Parts of the polymer per 100 parts of the pigment circltn:circulation Pigment Dispersion Liquid 14 15 16 17 18 19 20 Pigment Kindof Pigment A A A A A A Modified A Polymer Kind of Polymer D E F A A APolymer- bonded Acid Value [mgKOH/g] 160 45 315 195 195 195 — Wt-av.Molecular Weght 8,600 8,600 9,200 9,000 9,000 9,000 — Mixed Amount (*1)50 50 50 30 300 350 25 Dispersion Viscosity in Step 1 [mPa · s] 200 300180 150 250 280 100 Conditions Dispersion Apparatus in Step 2 CLM CLMCLM CLM CLM CLM CLM Viscosity in Step 2 [mPa · s] 100 130 90 80 150 16080 Integrated Power in Step 2 0.75 0.75 0.75 0.75 0.75 0.75 0.75[kWh/kg] Operation Mode in Step 2 circltn circltn circltn circltncircltn circltn circltn Dispersion Apparatus in Step 3 BM BM BM BM BM BMBM Operation Mode in Step 3 circltn circltn circltn circltn circltncircltn circltn Medium Diameter in Step 3 0.1 0.1 0.1 0.1 0.1 0.1 0.1[mm] Properties Primary Particle Diameter D 110 110 110 110 110 110 110of [nm] Pigment D₅₀ [a · snm] 112 145 115 128 118 132 115 D₉₀ [a · snm]212 293 173 250 190 243 217 D₉₀/D₅₀ 1.9 2.0 1.5 2.0 1.6 1.8 1.9 PigmentDispersion Liquid 21 22 23 24 25 26 Pigment Kind of Pigment A A A A A APolymer Kind of Polymer A A A A A A Acid Value [mgKOH/g] 195 195 195 195195 195 Wt-av. Molecular Weght 9,000 9,000 9,000 9,000 9,000 9,000 MixedAmount (*1) 5 4.8 50 50 50 50 Dispersion Viscosity in Step 1 [mPa · s]110 100 200 200 200 200 Conditions Dispersion Apparatus in Step 2 CLMCLM CLM CLM CLM CLM Viscosity in Step 2 [mPa · s] 55 50 10 10 10 100Integrated Power in Step 2 0.75 0.75 0.30 0.30 1.50 0.75 [kWh/kg]Operation Mode in Step 2 circltn circltn circltn circltn circltn circltnDispersion Apparatus in Step 3 BM BM BM BM BM — Operation Mode in Step 3circltn circltn pass pass pass — Medium Diameter in Step 3 0.1 0.1 0.20.1 0.05 — [mm] Properties Primary Particle Diameter D 110 110 110 110110 110 of [nm] Pigment D₅₀ [a · snm] 140 140 155 115 98 300 D₉₀ [a ·snm] 278 293 377 308 194 1000 D₉₀/D₅₀ 2.0 2.1 2.4 2.7 2.0 3.3 (*1) Partsof the resin per 100 parts of the pigment circltn: circulation

<Preparation of Ink>

The ink was prepared by mixing sufficiently the pigment dispersionliquid and the components shown in Table 2, and pressure-filtering themixture through a micro-filter (Fuji Film Co.) having a pore size of 1.0μm.

TABLE 2 Composition of Ink (Unit of upper columns: %) Examples 1 2 3 4 56 7 8 9 10 Pigment Dispersion Liquid 1 6.7 Pigment Dispersion Liquid 26.7 Pigment Dispersion Liquid 3 6.7 Pigment Dispersion Liquid 4 6.7Pigment Dispersion Liquid 5 6.7 Pigment Dispersion Liquid 6 6.7 PigmentDispersion Liquid 7 6.7 Pigment Dispersion Liquid 8 6.7 PigmentDispersion Liquid 9 6.7 Pigment Dispersion Liquid 10 6.7 PigmentDispersion Liquid 11 Pigment Dispersion Liquid 12 Pigment DispersionLiquid 13 Pigment Dispersion Liquid 14 Pigment Dispersion Liquid 15Pigment Dispersion Liquid 16 Pigment Dispersion Liquid 17 PigmentDispersion Liquid 18 Pigment Dispersion Liquid 19 Pigment DispersionLiquid 20 Pigment Dispersion Liquid 21 Pigment Dispersion Liquid 22Pigment Dispersion Liquid 23 Pigment Dispersion Liquid 24 PigmentDispersion Liquid 25 Pigment Dispersion Liquid 26 Glycerin 2.5 2.5 2.52.5 2.5 2.5 2.5 2.5 2.5 2.5 2-Pyrrolidone 2.5 2.5 2.5 2.5 2.5 2.5 2.52.5 2.5 2.5 Polyethylene Glycol (*1) 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.04.0 Acethylenol E100 (*2) 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5Ion-Exchanged Water 83.8 83.8 83.8 83.8 83.8 83.8 83.8 83.8 83.8 83.8Pigment Content [%] 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 PolymerContent [%] 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Pigment/PolymerRatio (*3} 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Examples 11 12 13 1415 16 17 18 19 20 Pigment Dispersion Liquid 1 Pigment Dispersion Liquid2 Pigment Dispersion Liquid 3 Pigment Dispersion Liquid 4 PigmentDispersion Liquid 5 Pigment Dispersion Liquid 6 Pigment DispersionLiquid 7 Pigment Dispersion Liquid 8 Pigment Dispersion Liquid 9 PigmentDispersion Liquid 10 Pigment Dispersion Liquid 11 6.7 Pigment DispersionLiquid 12 6.7 Pigment Dispersion Liquid 13 6.7 Pigment Dispersion Liquid14 6.7 Pigment Dispersion Liquid 15 6.7 Pigment Dispersion Liquid 16 6.7Pigment Dispersion Liquid 17 6.7 Pigment Dispersion Liquid 18 13.0Pigment Dispersion Liquid 19 13.0 Pigment Dispersion Liquid 20 20.0Pigment Dispersion Liquid 21 Pigment Dispersion Liquid 22 PigmentDispersion Liquid 23 Pigment Dispersion Liquid 24 Pigment DispersionLiquid 25 Pigment Dispersion Liquid 26 Glycerin 2.5 2.5 2.5 2.5 2.5 2.52.5 2.5 2.5 2.5 2-Pyrrolidone 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5Polyethylene Glycol (*1) 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0Acethylenol E100 (*2) 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5Ion-Exchanged Water 83.8 83.8 83.8 83.8 83.8 83.8 83.8 77.5 77.5 70.5Pigment Content [%] 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 PolymerContent [%] 1.0 1.0 1.0 1.0 1.0 1.0 0.6 6.0 7.0 — Pigment/Polymer Ratio(*3) 2.0 2.0 2.0 2.0 2.0 2.0 3.3 0.33 0.29 — Examples ComparativeExamples 21 22 1 2 3 4 Pigment Dispersion Liquid 1 Pigment DispersionLiquid 2 Pigment Dispersion Liquid 3 Pigment Dispersion Liquid 4 PigmentDispersion Liquid 5 Pigment Dispersion Liquid 6 Pigment DispersionLiquid 7 Pigment Dispersion Liquid 8 Pigment Dispersion Liquid 9 PigmentDispersion Liquid 10 Pigment Dispersion Liquid 11 Pigment DispersionLiquid 12 Pigment Dispersion Liquid 13 Pigment Dispersion Liquid 14Pigment Dispersion Liquid 15 Pigment Dispersion Liquid 16 PigmentDispersion Liquid 17 Pigment Dispersion Liquid 18 Pigment DispersionLiquid 19 Pigment Dispersion Liquid 20 Pigment Dispersion Liquid 21 6.7Pigment Dispersion Liquid 22 6.7 Pigment Dispersion Liquid 23 20.0Pigment Dispersion Liquid 24 20.0 Pigment Dispersion Liquid 25 20.0Pigment Dispersion Liquid 26 6.7 Glycerin 2.5 2.5 2.5 2.5 2.5 2.52-Pyrrolidone 2.5 2.5 2.5 2.5 2.5 2.5 Polyethylene Glycol (*1) 4.0 4.04.0 4.0 4.0 4.0 Acethylenol E100 (*2) 0.5 0.5 0.5 0.5 0.5 0.5Ion-Exchanged Water 83.8 83.8 70.5 70.5 70.5 83.8 Pigment Content [%]2.0 2.0 2.0 2.0 2.0 2.0 Polymer Content [%] 0.2 0.19 1.0 1.0 1.0 1.0Pigment/Polymer Ratio (*3} 10.0 10.3 2.0 2.0 2.0 2.0 (*1) AverageMolecular weight 1,000 (*2) Surfactant (Kawaken Fine Chemical Co.) (*3)Pigment Content/Polymer Content

<Evaluation>

The ink obtained as above was filled in an ink cartridge. The cartridgewas mounted on an ink jet recording apparatus BJ-F900 (Canon K.K.) whichejects ink by action of thermal energy. With this ink jet recordingapparatus, recording was conducted with solid print portions atrecording duties of from 10% to 200% by steps of 10% on a glossyrecording medium (Super-photo-paper SP-101: Canon K.K.). The printerdriver mode was selected to be in a photo paper pro mode. The setting ofthe photo paper pro mode was a below:

Kind of paper: Photo Paper Pro

Printing quality: Fine

Color adjustment: Automatic

(Storage Stability)

The ink was enclosed tightly in a Shot bottle, and was stored in an ovenat 60° C. for 2 weeks. The viscosities before and after the storage weremeasured with an E-type viscometer (RE80L: Toyo Seiki K.K.). The storagestability was evaluated by the percentage change of the viscosity by thestorage in view the evaluation standards below. Table 3 shows theevaluation results. In the present invention, the stability of Level Bor more is considered to be acceptable. Level A is excellent, and LevelC is not acceptable.

A: The viscosity change is less than 15%

B: The viscosity change is 15% or more to less than 30%

C: The viscosity change is 30% or more

(Chroma)

One day after the recording, the chroma of a magenta image was measuredwith a tester Spectrolino (Gretag Macbeth Co.) for the evaluation. Thechroma can be derived by the equation:c*={(a*)²+(b*)²}^(1/2)

The chroma was evaluated by the evaluation standard below. Table 3 showsthe evaluation results. In the present invention, with the evaluationstandard below, Level B or more is acceptable, Level A is excellent,Level AA is especially excellent, and Level C is not acceptable.

AA: c* is 84 or more

A: c* is 82 or more to less than 84

B: c* is 80 or more to less than 82

C: c* is less than 80

(Glossiness)

The glossiness level (20° gloss) of the recorded matter was measuredwith a microhazemater (BYK Gardner Co.). The glossiness level of therecorded matter was evaluated by the average of the glossiness level ofthe images formed at the prescribed duty levels. Table 3 shows theevaluation results. In the present invention, with the evaluationstandard below, Level B or more is acceptable, Level A is excellent,Level AA is especially excellent, and Level C is not acceptable.

AA: The glossiness level (20° gloss) is 60 or more

A: The glossiness level (20° gloss) is 50 or more to less than 60

B: The glossiness level (20° gloss) is 40 or more to less than 50

C: The glossiness level (20° gloss) is less than 40

TABLE 3 Evaluation Results Storage Stability Chroma Glossiness Examples1 A AA A 2 A A AA 3 A A B 4 A AA AA 5 A B B 6 A A A 7 A A A 8 B AA A 9 AA A 10 A B A 11 B A A 12 B AA AA 13 A A AA 14 A A A 15 B A A 16 B A AA17 A AA A 18 A AA A 19 A A A 20 A A A 21 A A B 22 B A B Comparative 1 BC C Examples 2 B C C 3 C A A 4 C C C

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2009-024615, filed Feb. 5, 2009, which is hereby incorporated byreference herein in its entirety.

1. An ink comprising a pigment, wherein the pigment comprises C.I. Pigment Red 282, and a primary particle diameter D (nm) of the pigment and a 50%-cumulative diameter D₅₀ (nm) in particle diameter distribution of the pigment satisfy a relation of D×0.95≦D₅₀≦150, and a 90%-cumulative diameter D₉₀ (nm) in particle diameter distribution of the pigment and the 50%-cumulative diameter D₅₀ (nm) satisfy a relation of 1.5≦D₉₀/D₅₀≦2.5.
 2. The ink according to claim 1, wherein the diameter D (nm) is 50 nm or more to 130 nm or less.
 3. The ink according to claim 1, wherein the 90%-cumulative diameter D₉₀ (nm) and the 50%-cumulative diameter D₅₀ (nm) satisfy a relation of 1.5≦D₉₀/D₅₀≦2.0.
 4. The ink according to claim 1, wherein the ink further comprises a polymer, the polymer having an acid value of 50 mgKOH/g or more to 300 mgKOH/g or less.
 5. The ink according to claim 4, wherein the polymer has a nonionic unit.
 6. The ink according to claim 4, wherein a content (mass %) of the pigment with respect to the total mass of the ink is 0.30 times or more to 10.0 times or less a content (mass %) of the polymer with respect to the total mass of the ink.
 7. The ink according to claim 1, wherein the pigment has a polymer bonded to the surface of the particles of the pigment.
 8. An ink jet recording method comprising ejecting an ink by an ink jet system to perform recording on a recording medium, wherein the ink according to claim 1 is used as the ink.
 9. An ink cartridge having an ink storage portion storing an ink, wherein the ink is the ink according to claim
 1. 10. An ink jet recording apparatus having an ink storage portion storing an ink and a recording head for ejecting the ink, wherein the ink according to claim 1 is used as the ink.
 11. The ink according to claim 1, wherein the ink is an aqueous ink. 